Expansible mandrel for driving molds for concrete piles



w. H. coal 2,88

EXPANSIBLE MANDREL FOR DRIVING MOLDS FOR CONCRETE FILES April 14,1959

5 Sheets-Sheet 1 Filed "Jan. 31, 1955 W. H. COB! April 14, 1959EXPANSIBLE MANDREL FOR DRIVING MOLDS FOR CONCRETE PILES 5 Sheets-Sheet 5Filed Jan. 51, 1955 W. H. CO BI April 14, 1959 FOR CONCRETE FILESEXPANSIBLE MANDREL FOR DRIVING MOLDS 5 Sheets-Sheet 4 Filed Jan. 31,1955 April 14, 1959 w. H. coal I 2,881,593

EXPANSIBLE MANDREL FOR DRIVING MOLDS FOR CONCRETE FILES Filed Jan. 51,1955 5 Sheets-Sheet 5 United States Patent EXPANSIBLE MANDREL FORDRIVING MOLDS FOR CONCRETE PILES Walter H. Cobi, Port Chester, N.Y.,assignor to Pneumatic Pile Corporation, New York, N.Y., a corporation ofNew York Application January 31, 1955, Serial No. 484,898 7 Claims. (Cl.61-79) The invention relates to expansible pile driving mandrels, andparticularly to expansible and contractable mandrels or cores capable ofinsertion into the empty shell or mold for a concrete or cast-in-placepile and of driving the shell into the ground under hammer blows.

The invention particularly relates to mandrels of this type which havecome to be known as pneumatic mandrels, and in which the expansion iscaused by the application of fluid pressure to container means withinthe mandrel.

It is a principal object of the invention to provide a mandrel of thepneumatic type, comprising annularly arranged metallic segments orsectors contacting during operation the inner surface of the shell ormold, and in which the forces from the hammer blows are substantiallyevenly distributed over the cross-sectional area of the mandrel at anypoint along its length, thereby insuring substantially straightlinedriving of the strata.

It is another object of the invention to provide such a mandrel in whichthe longitudinal elements will be firmly positioned within the shell inthe expanded condition of the mandrel to insure stable operation.

It is a further object to provide an expansible and contractable mandrelwhich can be effectively expanded by a lower fluid pressure per unitarea than in previous arrangements.

It is a more specific object to provide stronger, inflatable, flexiblecontainer means than was previously provided for expanding the mandrel,and which is subject to less wear by depending for effective action upona change of the cross-sectional shape from deflated to inflatedcondition and by substantially avoiding any expansionor stretching ofthe wall material of the container during such action.

It is still another object to simplify the construction and assemblageof such a mandrel by reducing the number of parts and simplifying theiradjustments for operation.

In accordance with a preferred form of the invention, the mandrel ismade up of a series of annularly arranged metallic segments, which maybe quadrants, disposed throughout the length of the mandrel forcontacting the inner surface of the shell of the pile, and of acentrally disposed flexible container means for the pressure fluidadapted to apply radially effective pressures to the surroundingsegments, when inflated.

In accordance with a principal feature of the invention the annuallyarranged metallic segments and the centrally disposed container meanshave cross-sectional areas shaped in such a manner that during inflationthe container means will engage the segments under pressure over areasof greater width than has hitherto been possible, one advantage beingthat the specific pressure necessary to effect the required contactpressure between segments and pile shell need only be very low ascompared with present practice. This reduces the strength requirementsand the pile into the ground, at least to the extent permitted by thenature of demand on associated equipment, and greatly simplifiesoperation.

In accordance with an associated feature of the invention the saidflexible container means is in the form of a long tubing ofsubstantially non-elastic wall material and has, when normally deflated,an inherent configuration of cross-sectional area which includes aplurality of contacting or pressure portions alternated with flexiblefold portions.

This permits considerable expansion of the tubing from deflated toinflated condition without any substantial elastic stretching of thewall material and consequent wear against the contacting metal.

In accordance with another related feature the said metallic segmentsare shaped cross-sectionally to each present to the container means aninner surface of considerable width through substantially the wholelength of the mandrel, so that the corresponding surface portions of thecontainer means may lay themselves flexibly against those inner metallicsurfaces during inflation and thus distribute the fluid pressure evenlyover said inner surfaces. One very important advantage of this is thepossibility it affords of shaping the opposed surfaces properly so thatthe circumferential width of the effective pressure areas may remainconstant during the inflating action or may even increase considerably.

In accordance with still another feature of the invention the tubing orcontainer for the fluid pressure is built up of a plurality ofcomparatively short manufacturing lengths which, since thecross-sectional shape of the tubing does not readily lend itself todirect joining, are terminated in suitable pairs of caps, each pairbeing supported in distinct junction sectors incorporated in themetallic segments, one sector in each, and joined by suitable pieces ofhose to pass the pressure fluid between adjacent lengths of tubing. Thesupport of tached tubing lengths is constructed to permit the radialmovements of the outer junction sectors with their joined segments.

Other features and advantages of the invention will be apparent from thefollowing detailed description.

This description should be read in conjunction with the attacheddrawings, which show a preferred embodiment of the invention. It shouldhowever be understood that the invention is not limited by the terms orexpressions used in this description, nor by the specific details orarrangements of parts shown in the drawing. The scope of the inventionin its various aspects is defined by the attached claims.

In the drawings:

Fig. 1 is a vertical sectional view of the upper portion of the.expansible mandrel or core showing the mandrel in place within the upperportion of the shell or mold and expanded ready for use;

Fig. 2 is a similar vertical view of a middle portion and the lowerportion of the mandrel;

The sections of Figs. 1 and 2 are taken along a diametrical planethrough the mandrel, as indicated by line 2- -2 in Figs. 4, 5 and 6.

Fig. 3 is a similar vertical sectional view of the middle portion of themandrel shown in Fig. 2 but shown here in contracted condition, thissection being taken along a plane indicated by line 33 in Fig. 7;

Fig. 4 is a cross-sectional View taken along line 4-4 in Figs. 1, 2 and8;

Fig. 5 is a cross-sectional view taken along line 55 in Figs. 1, 2 and8;

Fig. 6 is a cross-sectional view taken along line 6-6 in Figs. 2 and 8;

Fig. 7 is a cross-sectional view similar to Fig. 6, except that it showsthe mandrel in contracted condition, and may be considered as takenalong line 77 in Fig. 3

the central caps and their at- Fig. 8 is a detailed verticalcross-sectional view taken along line 8- 8 in Figs. 4, 5 and 6.

The drawings show in general an expanded mandrel in 'operative positionwithin-apile shell or mold 10, except for Figsf3 and 7 which show themandrelcontracted within the shell 10. The shell isof the corrugatedtype, having corrugations running parallel-around the shell and-inimmediate succession along the entire length; which corrugations may, ifdesired,- be-helical.

'In the embodiment shown in the drawing'the mandrel is made upoffoursimilar segments or quadrants 12, 14, 16, 18 which extend throughsubstantially the entire length of the mandrel. Through most-of thelength of the-mandrel each segment includes a .u-shaped channelmember-21 and an outer curved-plate-22which is welded along its entirelength to the two edges of the channel member 21, as willappearfrom-Figs.-6 and 7. The member 21- and the,plate 22may-be ofsteeldrawn or otherwise formed to the desiredshapes and dimens'ions. Both themembers 21 and the plates .22 receive the force from the-hammer blows attheir upper ends and transmit the force through their entire length tothe bottom end of the mandrel. When the length of the mandrel, asrequired for any particular job, exceeds the manufacturing lengths ofthese members and plates, successive portions are welded or boltedtogether'endwise, so that each segment formsa continuous structure.

The channel members 21, being welded along thesedges of the plates 22,extend their backs 24 inwardly toward the centrally located pressurecontainer or tubing 30, where theypresent aslightly curved surface 26continuously in contact with tubing 30 along itsientire length.

As can be seen in Fig. 6 where thefour metallic segments or sectors areshown in the expanded condition of the mandrel and in contact with theshell .10, the four plates 22 are separated byspaces23 between theiredges, which allow for the contraction of themandrel, .as'shown in Figs.3 and 7.

The tubular container 30 is shown in inflated condition inFig. 6 and indeflated condition inFig. 7, the views showing the correspondingcross-sectional configurations of the container wall under the twoconditions.

"When deflated the tubing 30 has a generally tubular shape which mayapproach the cylindrical shape. It has four-external pressure portions'or-surfaces 32, 34, 36, and38 separatedby four fairly deep folds orgrooves 39 throughout its length (see also- Fig. 3).

The wall in thepreferred form of the container comprises:an outerlayer-42am an innerv layer 44- of flexible material: and an intermediatelayer=46 of strands. of thin strong yarn properly'wovenor spun about theinner layer to form a practically non-elastic reenforcement for thewall. The strands are preferably of nylon. The material in layers :42and 44 is preferably of a rubberlike composition capable of heatcuringfor imparting thereto an inherent or cured-in tendency to retain, afterfinal curing, any particular wall thickness and wall shape given theretoduring curing. This material may include rubber, neoprene, Buna or othersimilar substances in any'su'itable proportions.

The shape shown in Fig. 7 may be termed that of a four-leaf clover.

When inflated the'tubing 30 will assume a shape which in part conformsto the shape of the confining metal elements and in part is that of aself-sustained wall portion. In the present instance the shape ispractically cylindrical, as shown in Fig. 6.

For structural and other reasons it has been found desirable tomanufacture the tubing30 in lengthsof -12 feet.

Fob-this, purpose, and in accordance with-a further feature of theinvention, a junction section is provided for joining adjacent tubingsectionswithin a unit mandrel.

A junction section 50-Iis shownin 'Fi gs.--2' and '3 under inflated and'deflated: 'conditions,- respectively. Some tde- 4% tails of the sectionare shown in Fig. 8 and cross-sections are shown in Figs. 4 and 5.

Through the length of the section the four channel members 21 arereplaced by four iron sectors 51, which may be castings, each of whichis shaped with an outer curved surface 52 conforming to and contactingthe inner surface of the plate 22 and with an inner curved surface 54which together with the other three surfaces 54provides a hollow spacewithin the mandrel. Each casting 51 is welded at its two ends to theadjacent channel mem bers 21, and in manufacture these castings andmembers may be placed as a unit within the much longer associatedcurved,.plate 22 and welded thereto along the edges of the plate in acontinuous manner. 'Thus the sector 51 is fitted in as a rigidcontinuationlinto the quadrant for extending the hammer blows throughthe mandrel.

The adjacent ends of two successive lengths of the tubing 30 :areterminated within thehollowtspace of the junction between surfaces 54.As will: appearifrom Fig. 8 the end of the tubing is closed by asuitable sealingcap assembly 60, comprising inner and outer rings 62,64, and a plug 66.

Specifically, the end of the tubing in fully inflated shape is shown inFig. 8 as clamped between a shouldered ring 62 having an inside surfacewith shallow grooves, and an inner ring 64 forcibly expanded forairtight sealing. The shoulder portion of ring 62 has an inner threadinto which is screwed the end portion 67 of the plug 66, this jointbeing made airtight bythe packing "68. The .end portion 67 has a deepexternal groove 70 into which extends a projection 72 from thesurface.54;ofreach.iof the castings 51, (see also Fig. 5), theseprojections .being disposed in a transverse plane so thatthey mayreadily slide in and out of the groove as themandrel'is deflated v andinflated.

Across the groove 70, and locatedinthe horizontal spaces between theprojections 72 from the four quadrants, are vertical posts 73 (Fig. 5),which-arese'cured in the plug section 66 of the cap and thus serve toprevent rotation of the cap.

The plug 66 has a series of bores 74 for connecting the interior of thetubing 30 to a pair of hose taps 76, and pieces of hose 78 connectbetween the taps :on the two caps 60 located within the samejunctionsection thereby establishing a continued circuit for thepressure fluid to all container sections 30.

The surfaces 54 are. inclined inwardly at each end of the. junctionsectionfor lining up with-the inner surfaces 26 of the adjacent channelmembers' ZI. The largest diameterof surfaces 54' is large enoughto'permit'the junction sections .51 to close in about the caps 60-at fulldeflationv of the mandrel without interference.

It may thus be observed that a plurality of-junction sections may bedistributed at uniform intervalsofsay 12'14' in the interior of amandrel with a length of tubing 30 stretched in each interva1 betweenthe junctions.

With the grooves of the two end caps fitted in over correspondingprojections 72 a length of tubing'30 will be suspended within themandrel and may be stretched to a desired tautness, the length of thetubing being lightly guided along the surfaces 26 between'successivejunction sections 50 both in inflated and deflated condition, asindicated in Figs. 6 and 7.

At the bottom end of the mandrel, as shown in Fig. 2, a termination ofthe mandrel and container'may be made by means of a junction'section 90,practically identical with the upper half of the junction section 50 andincluding four sectors or castings '91, which may conveniently .bewelded at their upper "ends to the adjacent channel 'members20. Thehose'taps 96"in' the container cap 60 at the lower end-of the 'tubing'30in said junction section 91 are plugged tight 'for terminationof'thepressure fluid circuit.

At the top end of the mandrel, as shown in Fig. 1, a special termination100 is used, the lower portion of which may be of the same constructionas that of the lower half of the junction 50. In this instance thecastings 101, corresponding to the castings 51, are extended upward intoheavy end portions 102 connected to the mandrel head 110. The uppermostcontainer cap 60 has two hose connections 104 through bores in endportions 102 to outer hose nipples 106 to which hoses from the pressurerig are attached, only one set of these hoses appearing in Fig. 1.

The entire mandrel may thus be visualized as comprising the top section100, a series of junction sections 50, bottom section 90 and a pluralityof main sections therebetween. The outer curved plates 22 may extendcontinuously from the top section 100 to the bottom section 90. Thejunction sections may be 12 to 14' apart, and may extend the samedistance from the top and bottom ends. The spaces between said junctionsections are occupied by the tubing sections 30, and by the channelmembers 21 within the quadrants, constituting the main sections.

For usual practice, the expanded mandrel may be 16" in diameter with aninflated center tubing of 3 /2"5" in diameter.

This entire structure is held together by bolts 111 and springs 112which also permit and limit its expansion and contraction. It has beencustomary with prior constructions to distribute such bolts fairlyevenly along the length of the mandrel. In accordance With the inventionthe bolts 111 with their individual springs groups at the top, bottomand junction sections. Such spacing along the mandrel is justified bythe stiffness of the quadrants secured by the spokelike effect of thechannel members 21 and the curvature and heavy thickness of theplates22, which also are needed for the proper trans mission of the hammerblows.

Referring, for example, to Fig. 2 it will be seen that the adjacent capterminations 60 of the container sections 30 are separated sufficientlyin the lengthwise direction to give room for a group of crossing bolts111. A ridge 114 rises from the inner surface 54 of each quadrant, theridge being high and wide enough to provide for the location of springsand bolt heads, as further illustrated in Figs; 4 and 8. The bolts areprovided in pairs crossing at 90 between oposed quadrants. As shownparticularly in Fig. 4, a spring 112 lies under the head of a bolt 111in one quadrant while another spring 112 lies under a nut on that boltin'the opposite quadrant. The total length of the bolt is such that thebolt does not project beyond the outer surface of the mandrel incontracted condition. The size and number of bolts through the mandrelwill of course be determined by the diameter of the mandrel and thedimensions of the structural elements. Since the bolts and springs arelast to be inserted in the assembling of the mandrel, holes 116 aredrilled in the outer plates 22 for their passage and also to provideadditional space for the bolt ends during contracted condition of themandrel.

' As illustrated in Figs. 1 and 2, suflicient space is also providedbeyond the end caps 60 and the respective upper and lower ends of themandrel to accommodate bolts 112 in the top and bottom sections 100 and90, respec tively.

In'the contracted condition of the mandrel, the springs 112 still havesufiicient compression to force the edges of adjacent plates. 22 intofirm contact with each other, thereby insuring the safe insertion intoand removal from the pile shell 10 of the whole mandrel.

From the foregoing description it may be seen that in deflated conditionof the tubing 30 the springs 112 will hold the quadrants in closedmutual contact and in contact with the effective surfaces 32, 34, 36, 38of the tubings 30. Under this condition the tubing will nearly assumeits cured-in shape. Or it may, if desired, be

112 are bunched in i slightly too large and be compressed by the springsunder this condition, thereby reducing the required depth of the folds39 in the relaxed or cured-in shape.

With the cross-section of the tubing having the shape of a four-leafclover, the effective surfaces or pressure areas engaging the juxtaposedmetal surfaces 24 may have an appreciable width as indicated by thespace W in Fig. 7. With the admission of fluid, usually air, underpressure the containers will be inflated causing the mandrel to expanduntil the plates 21 press against the inside of the shell 10. Thepressure may then be further increased to insure firm contact betweenmandrel and shell. At this time the extra portions of the container wallin the longitudinal folds between the effective surfaces W will supplywall material enough to permit the tubing to take a greatly expandedshape which is practically cylindrical and which permits fullutilization of the iron surfaces 26, with a contact width W. Thiscontact width may with careful design be about -75% of the totalexpanded surface of the expanded tubing. Thus with a tubing diameter ofabout 4 inches and a mandrel diameter of about 10 inches the ratio ofspecific pressures at the two surfaces of tubing and mandrel mayapproach the 10 to 4 value.

While the pressure thereafter is being withdrawn for relaxation of themandrel, the inherent tendency of the wall material will cause the foldportions to cave in first and gradually assume their full depth as thepressure portions resume their natural diameter.

In prior pressure containers, as represented by Patents 2,313,625,issued March 9, 1943, and 2,635,015, issued January 13, 1953, to thepresent inventor and employed by him to considerable extent, the centralcontainer element was complicated by the use of a tubing which was ofelastic material and required a flexible essentially nonelastic wrapperinterposed between the tubing and the mandrel quadrants to withstand thehigh concentrated pressures from the narrow contact areas presented bythe quadrants. In contrast, the present invention utilizes a strong andsubstantially non-elastic wall for the container, which thus not onlyhas ample strength to receive the contact pressure, but particularly iscapable of sustaining the inner pressure over the unsupported areasbetween the channel numbers 21. The use of unelastic material is madepossible by the introduction of extra wall area in the folds between thecontact areas. The contrast with the prior art, referred to, isemphasized by the greatly increased effective contact area in expandedcondition which permits a much lower pressure per unit area for a givenpressure between mandrel and shell. This is secured particularly by theincrease of the container diameter relative to mandrel diameter, whichin turn permits a reshaping of the quadrant structure to present widercontact areas.

A further advantage of the use of substantially nonelastic wall materialis found in the fact that there will be close adherence, which almostresembles an adhesion, between the contacting surfaces of the plasticcontainer and the metallic channel members. Thus there will be little,if any, tendency to relative shifting between the opposed surfaceseither in the transverse or the longitudinal direction during expansionand contraction. Thus, when this adherence is left undisturbed therewill be little, if any, rubbing action between the opposed surfaces dueto the violent vibrations during driving operations with a consequentreduction, if not elimination, of

wear.

It has before been proposed to use certain types of firehose with anouter cord layer for pressure containers in driving mandrels of thisgeneral type. Such hose has however been found to change its length by10% or more between inflated and deflated conditions. Such elastic hose,when fastened at both ends in a mandrel, would thus crimp up badlyduring expansion, and would be pinched between the quadrants duringdeflation, soon resulting in cuts in the'hose wall. In accordance withthe present invention the'tubing'is suspended between the tightlysecured end caps which in turn are held in position by the projections72..from the quadrant elements, and may thus be kept tight both inexpanded and contracted condition because of the slight elasticity ofthe wall material, with the chance of cutting being eliminated.

Though the present embodiment of the invention is shown and describedherein as a mandrel comprising four longitudinal segments or sectorswith four pressure surfaces engaging a pressure container having fourexpansion folds between those surfaces, it should be understood that,withouta 'departure'from the spirit and scope ofz'the invention, the'mandrel may comprise six segments'with six pressure surfaces engaging acentral con tainer'with three or six expansion folds between surfaces,or maycomprise a larger number of segments.

Itshould also be understood that the number of effective'surfacespresented by the mandrel segments and by the central containerneed notbe the same. Thus a tubing with three effective surfaces may be usedwith mandrels having three, four, 'five'or six segments. In such case itmay be desirable to twist each length of tubing, one or two turns, or ahalf turn, for example, to evenly distribute the contact areas.

It should further be understood that the shape of the plates 22 engagingthe inner surface of the shell may differ from that shown in the drawingand may be made to conform to other shapes of the shell than thecircular shape shown. Thus, the plates may be flat to conform with asquare shell, or they maybe of an angular crosssection to conform withpolygonal cross-sections of a shell with more than four corners.

When the grooves'of the corrugated shell are distributed helically, theplates 22 may have welded to their outer surfaces a series of half roundhelix bars 122 (Fig. 8) for engagement with such grooves. The bars maybe placed at intervals of, for example, about a foot along the 'lengthof the mandrel. By this means the driving force of the hammer blows maybe well distributed over the Whole length of the shell to overcome thefriction with the ground during driving.

Considering now more specific features of the mandrel illustrated, itmay be noted that the top assembly of the mandrel includes the drivehead 110 (shown in Fig. l) which is in the form of a cylindrical blockwith a de pression 131 in the top surface for receiving the-metalencased wooden hammencu'shion 132, and with a depression 133 in thebottom surface fitting loosely over the end portion 102 of the mandrel.The head has two parallel holes 134 through the body portion thereof toreceive steel cables for raising and lowering the whole mandrel.

Two mild steel bufler plates 135 .are positioned against the bottom ofthe depression 133 and engage the upper aligned end surfaces of theendportions 102 for evenly distributing the hammer blows to theseelements during operation.

The drive head 110 is loosely connected to the upper end of themandrelproper by a lifting bolt 140 fastened in ancentral hole 141 inthe:drive head by means .of spherically surfaced washers 142, 143 heldagainst spherically surfaced shoulders in the hole 141 by a nut 144 onthe shouldered bolt:140.

The lower end of the bolt extends a short distance into the .interiorofthe mandrel where it carries a spider 145 having axhub portion forfastening to the bolt and two pairs'offlat Wings 146, 147-extending intothe spaces 24 between the endportions 102. As may be seen in Fig. l,the'wings 146extendin under' and clear a pair of crossbol'ts 148 whichcrossthe spaces 24 and pass through holes in the'opposed faces of theend portion 102. Anothenpair ofcross-bolts, not 1 shown, are placed at a'8 lower level than the pair 148 to clear them and pass over wings 147.

The bottom assembly of the mandrel is contained by the lower end of theshell 10 and the boot 150 welded thereto, as shown in Fig. 2. The bootmay be of iron, and has an upper cylindrical portion 151 for protectionof the lower edge of the shell, a shoulder portion 152 for receiving ashare of the force from the junction sections 90, and a central cupportion 153holding a casting 154 with a top surface partly in abutmentwith the bottom of the junction sections toalso receive force therefrom.The casting. 154 is part of the mandrel proper, and has a central eyebolt 155 reaching up about the lower'crossbolt 111 in the junctionsection 90, so that it willfollow the remainder of.the.mandr'elinremoval from.and.insertion into the shell 10.

When the. mandrel islbeing. lifted out of a shell which has been drivenin place, a steel cable is passedthrough the holes 134 inthedriveflheadand up about'thelbase or the hammer, and the mandrel. is.lifted bodily up into the leads of the driving rig. After the drive headhas been raised a short distance, an inch or less, for example, the twopairs of wings 146, 147 will engage the corresponding pairs ofcross-bolts whereupon the entire mandrel will rise with the drive. head.

By means of the spherical mounting of the liftingbolt in the drivehead acertain freedom of. self-adjustment between'the drivehead and thetop ofthemandrel is available during therough. lifting. operations. Theupperand lower nuts on bolt 140 are preferably of the.type known as elasticstop nuts, whichlock themselves on to the bolt.

Mandrels of this type may be used under greatly varying conditions andwith shellsof greatly varying. lengths and cross-sections. Thedimensions of the mandreland its parts therefore may vary greatly. Themandrelmay bedesigned for shells 100 feet or more in length.

The fluid pressure is preferably obtained from anair compressor, and thepressure for the longest mandrels need not exceed 30 lbs. per squareinch. The compression springs maybe tensioned. to 300 lbs.

When the mandrel is collapsed, the half round bars 122 on its outsidesurface clear the inside of the corrug-ated shell by at least A" allaround, and the expansion may amount to an increase in diameter ofthemandrel of. an inch and ahalf or even. more. It will, of course beunderstood that the foregoing pressures and dimensions. are merelyexamples'of. thosethat may be-employed.

' There is somedemand for pile .driving mandrels which are tapered overthe lower part or over substantiallythe whole length. The pneumaticmandrel, constructedas described hereinbefore, lends itself to thetapered construction. This is,partly on account of its extremely simpleinterior construction. .If the mandrel is to be tapered, the tubings andthe end caps thereformay be kept at the .maximum dimensions used at thelargest diameter of the mandrel, and the tapering may besecured by thegradual reduction in dimensions of the longitudinal iron elements in thefour or six. sectors surrounding the tubing.

The terms and expressions which. I have employed are used as terms ofdescription and not of limitation, and I have no. intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but recognize .thatvarious modifications are possible within thescopeof the inventionclaimed.

I claim:

1. A driving mandrel for the shell of a pilewhichcomprises'aplurality oflongitudinal mainsections cachinclnding a centrally disposedexpansible'fluid pressurev container'having self-restoring, longitudinalfoldstand a pluralitybf'metal sectors disposed between .the shell..andsaid container, said man'drel'further comprising an expansible junctionsection disposed in each interval between adjacent main sections forjoining the containers and the metal sectors thereof, each junctionsection including a plurality of sector castings for joiningcorresponding metal sectors and a plurality of bolt and spring meansextending between diametrically opposed castings for contraction of saidmetal sectors about the containers in said main sections, each of saidcontainers in adjacent main sections including a pressure tight captermination having an outlet for a hose connection between the caps,said caps and hose being disposed within said junction section, and saidcaps being slidably fastened in said junction section to permittransverse expansion and contraction of the section and to permitlongitudinal tightening of the associated containers through the lengthof said main sections.

2. An expansible mandrel for insertion into a metal shell to receivehammer blows for driving the shell into the ground, said mandrelcomprising a plurality of elongate sections having a cross section ofgenerally sector shape, each of said sections having a curved rimportion engageable with the interior surface of said shell, each of saidsections having a channel portion comprising a pair of wings extendinginwardly from said rim portion toward the vertical central axis of themandrel and a pressure receiving wall of substantial width extendingtransversely between the inner ends of said inwardly extending wings andpositioned between said rim portion and said axis, said transversepressure receiving walls of said plurality of sections defining acentral opening the center of which is said axis, bolt means connectingsaid sections and spring means normally urging said sections inwardlytoward said axis, an elongate flexible pressure container mounted withinsaid central opening, said pressure container having a substantiallyunstretchable peripheral wall of rubber-like material having a pluralityof longitudinally disposed pressure portions and a longitudinallydisposed fold portion between each pair of adjacent pressure portions,each of said pressure portions lying in engagement with one of saidtransverse pressure receiving walls, said folds moving outwardly uponinflation of said pressure container thereby causing said pressurecontainer to expand without change in the peripheral and longitudinaldimensions of said container wall and said container wall thereby movingsaid pressure portions outwardly against said pressure receiving walls,causing said sections to move radially outward to engage said rims withsaid shell and, upon deflation, said folds resuming their inwardlyextending position to decrease the diameter of said container from itsexpanded condition thereby permitting said spring means to move saidsections radially inward out of contact with said shell.

3. An expansible mandrel for insertion into a metal shell to receivehammer blows for driving the shell into the ground, said mandrelcomprising a plurality of elongate sections of generally sector shape incross section, each of said sections having a curved rim portionengageable with the interior surface of said shell, each of saidsections having a channel portion comprising a pair of wings extendinginwardly from its rim portion toward the vertical central axis of saidmandrel and a pressure receiving wall of substantial width extendingtransversely between the inner ends of said wings and positioned betweensaid rim portion and said axis, said transverse pressure receiving wallsdefining a central opening the center of which is said axis, yieldablemeans connecting said sections and normally urging said sections towardsaid axis to move said sections to contracted position, an inflatableand deflatable elongate tubular flexible pressure container within saidcentral opening having a tubular peripheral wall surrounding saidvertical axis, said tubular wall of the pressure container extendingbetween said axis and said pressure receiving walls of said mandrelsections, said peripheral wall being made of substantially unstretchablerubber-like material and having a plurality of longitudinally disposedpressure-portions each of which engages a pressure receiving wall of oneof said sections and having a longitudinally disposed, inwardlyextending, fold between each pair of adjacent pressure portions, saidfolds moving outwardly upon inflation of said pressure container causingsaid pressure container to expand to increase its diameter withoutstretching of said peripheral wall thereby causing said pressureportions to move outwardly against said pressure receiving walls therebycausing said sections to move radially outward to cause said rimportions to engage the interior surface of said shell with clampingcontact and, upon deflation of said container, said folds resuming theirinwardly extending position to decrease the diameter of said containerfrom its expanded condition thereby permitting said sections to moveradially inward into contracted position, out of clamping contact withsaid shell.

4. An expansible mandrel for insertion into a metal pile shell toreceive hammer blows for driving the shell into the ground, said mandrelcomprising a plurality of elongate sections of generally sector shape incross section, each of said sections having a curved rim portionengageable with the interior surface of said shell, each of saidsections having a channel portion comprising a pair of wings extendinginwardly from the ends of its rim portion toward the vertical centralaxis of the mandrel and terminating short of said axis and each sectionhaving a pressure receiving wall of substantial width extendingtransversely between said wings from the inner ends of said wings, saidpressure receiving walls providing a longitudinal central opening, boltmeans connecting diametrically opposite sections, compression springs onsaid bolts urging said sections toward said axis, a flexible,inflatable, deflatable, elongate tubular pressure container mounted insaid central opening, the tubular peripheral wall of said containerbeing made of reinforced rubber material such that said tubular wall isunstretchable longitudinally and peripherally, said tubular wall havinglongitudinally disposed pressure areas, one for each of said pressurereceiving walls, and said tubular wall having a longitudinally disposedfold between each adjacent pair of pressure areas normally extendinginwardly, each of said pressure areas being in engagement with one ofthe transverse pressure receiving walls of said sections, means forintroducing fluid pressure into said container to inflate saidcontainer, said folds upon inflation of said container expandingoutwardly, without change in the peripheral dimensions of said containerwall and causing said pressure areas to exert pressure on said pressurereceiving walls to move said sections radially outward against the forceof said springs to move said rim portions against said shell, said foldsupon deflation of said container moving to their normal inwardlyextending position permitting said springs to move said sectionsinwardly away from said shell.

5. An expansible mandrel for insertion into a metal pile shell toreceive hammer blows for driving the shell into the ground, said mandrelcomprising a plurality of elongate sections having a generally sectorshape in cross section, each having a rim portion engageable with saidshell, each of said sections also having a channel portion comprising apair of wings extending inwardly from said rim portion toward thevertical central axis of the mandrel and an arcuate shaped pressurereceiving wall extending transversely between said inwardly extendingwings, said pressure receiving walls providing an elongate centralopening, an inflatable, deflatable, elongate, flexible tubular pressurecontainer having an unstretchable tubular wall of reinforced rubbermaterial surrounding said vertical axis and mounted in said centralopening, and said wall lying between said central axis and said pressurereceiving walls, said container tubular wall having a plurality oflongitudinally disposed pressure areas, each of which engages one ofsaid pressure receiving walls, and said tubular wall having alongitudinally disposed,'inwardly extending fold between each adjacentpair of pressure area s, bolts connecting opposed sections, spring meansmounted on said bolts normally urging said sectionstoward said axis,means for introducing fluid pressure into said pressure container, saidfolds expanding outwardly upon inflation of said container therebyincreasing the diameter of said container without stretching saidtubular wall, thereby increasing the diameter of said container andcausing said pres sure areas over a major portion of the periphery ofsaid tubular wall to press against said pressure receiving areas tocause said sections to move radially outward and thereby'force said rimportions against said shell, said folds returning to'their inwardlyextending positions on deflation .of said container to decrease thediameter of said container from its inflated condition therebypermitting said springs to return 'said sections inwardly away from saidshell.

'6. A mandrel constructed "according to claim 2 in which thepressurereceiving walls of said sections are arcuat'ely shaped.

7. A mandrel .constructed according to claim 6 in which there are foursections each having a cross section of "generally quadrant'sector shapeand in which the rim portion. of each section has an arcuate length ofapproximately 90 when said mandrel is in contracted position and inwhich said bolts extend diametrically to connect "diametrically oppositesections.

References Cited in the file of this patent UNITED STATES PATENTS865,653 Upson'et-al. July 5, 1932 2,170,188 Gobi ,Aug. 22, 19392,312,587 Price Mar. 2, 1943 2,313,625 Cobi Mar. 9, 1943 2;625,015 'CobiJan. 13, 1953 2,684,577 Smith Ju1y27, 1954

